This invention is in the field of printed wiring boards. The primary structure for assembling circuitry in the past was the use of a printed wiring board having through-holes for mounting components with attached leads. This technique imposes constraints on the component density that can be achieved. The restriction is in direct conflict with the trend toward smaller system packages that necessitate higher component density.
To relieve the leaded-package limitations, the industry has developed surface mount technology for IC packaging. This in turn has caused several problems for the printed wiring board. The first of these problems is increased heat that must be dissipated. Since the density of components has increased, then there is more thermal energy generated in a given surface area than there was using leaded technology. Therefore, the printed wiring board should provide some means for transporting the additional heat flux.
It is an object of the invention to provide a printed wiring board that functions as a heat-sink.
It is also an object of the invention to provide a structure allowing good thermal conductivity from an internal thermal plane to the exterior of the printed wiring board for removal of heat.
Another heat related problem is that of the difference in thermal coefficients between the components and the printed wiring board. The heat will cause both the individual components and the printed wiring board to expand. As there is a high probability that there is a difference in the rate of expansion. Therebetween, the solder joint between the component and the printed wiring board will be stressed. Also, deflection of the printed wiring board will produce stress in the solder joints.
It is therefore an object of the invention to have a printed wiring board structure that possesses similar thermal expansion characteristics to surface mount components to be attached.
These and other objects of the invention are achieved by: a printed wiring board adapted for mounting components thereto, said printed wiring board including:
a thermally conductive core for conducting heat generated by said components to a thermal interface region integral with said printed wiring board; and
said thermal interface region having a plurality of thermally conductive vias substantially extending from said thermally conductive core to the surface of said printed wiring board.